Apparatus for observing combustion conditions in a gas turbine engine

ABSTRACT

A fuel injector for a gas turbine combustor is disclosed which includes a feed arm having a flange for mounting the injector within the combustor and a fuel nozzle depending from the feed arm for injecting fuel into the combustor for combustion. An optical sensor array is operatively associated with the fuel nozzle for observing combustor flame characteristics. The optical sensor array includes a plurality of sapphire rods positioned to be close enough to the combustor flame to oxidize soot deposits thereon.

CROSS-REFERENCE TO RELATED APPLICATION

The subject application is a continuation-in-part of U.S. applicationSer. No. 10/841,765 filed May 7, 2004 now U.S. Pat. No. 7,334,413.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention is directed to optical sensors for gas turbineengines, and more particularly, to an apparatus, system and method forobserving the spectral and thermal characteristics of a flame in thecombustion chamber of a gas turbine engine to detect, in real-time,conditions indicative of combustion instabilities and the like.

2. Background of the Related Art

Combustion instability is a significant problem in the design oflow-emission, high performing combustion chambers for gas turbines,boilers, heaters and furnaces. Combustion instability is generallyunderstood as high amplitude pressure oscillations that occur as aresult of the turbulent nature of a combustion process and the largevolumetric energy release within the combustion chamber. Combustioninstability diminishes engine system performance, and the vibrationsresulting from pressure oscillations can damage hardware components,including the combustion chamber.

There are many factors that contribute to combustion instability withinthe combustion chamber of a gas turbine. These include, for example, thefuel content, fuel and/or air injection speed or inlet pressure,fuel/air concentration/ratio, temperature changes within the combustionchamber, the stability of the flame, large scale coherent flowstructures affecting mixing (i.e., vortex shedding), the coupling ofacoustic pressure waves with combustion heat release at combustorresonance frequencies, and/or extinction/re-ignition phenomenonoccurring at low flame temperature and high combustion pressure.

In the past, passive control methods were employed to correct combustioninstability, including, for example, modifying the fuel injectiondistribution pattern, or changing the shape or capacity of thecombustion chamber. Passive controls are often costly and limitcombustor performance. More recently, active controls have been used tocorrect combustion instability by modifying the pressure within thesystem and/or regulating the flow of fuel or air into the combustor inresponse to detected unstable conditions. An example of active controlis disclosed in U.S. Pat. No. 5,784,300 to Neumeier et al.

It has been determined through experimentation that direct observationof a combustor flame can provide information that may be used toactively control combustion instability. For example, combustion drivenpressure oscillations can be detected by observing flame movement andvariations in flame intensity. In addition, spectral radiationindicative of combustion by-products and emissions that effect flametemperature or other flame qualities may be observed. These observationsmay be analyzed and used by an active combustion control system toregulate the flow of fuel to the combustion chamber of a gas turbine oradjust the fuel/air ratio for combustion and thereby stabilize thecombustion process.

Optical sensors for observing combustion processes are known in theprior art, but they are limited in many respects. For example, U.S. Pat.No. 3,689,773 to Wheeler describes a flame monitoring system for afurnace wherein the flame is viewed from the side of the burner. Sincethe primary combustion zone within the burner is not stationary, theflame front can move out of the field of vision of the flame sensor.This can cause the system to obtain inaccurate measurements. U.S. Pat.No. 4,709,155 to Yamaguchi et al. describes an optical flame detectorfor use in a boiler that includes optical fibers protected from thermaldamage by a forced air-cooling system. Such a system would have limitedapplication in a gas turbine combustor where operating temperatures arefar in excess of those present in a boiler.

Clearly, there is a need in the art for an optical flame sensor that maybe used in active combustion control which overcomes the deficiencies ofprior art optical flame sensors. Moreover, there is a need in the artfor an optical flame sensor that may be employed in the combustionchamber of a gas turbine engine, which has a wide field of view so thatthe combustor flame will remain within the line of sight of the sensorat all times during the combustion process, and which does not requirecooling means to operate within the combustion chamber.

SUMMARY OF THE INVENTION

The subject invention is directed to an apparatus for observingconditions within the combustion chamber of a gas turbine engine. Moreparticularly, the subject invention is directed to a new and useful fuelinjector for a gas turbine engine that includes, among other things,optical sensing means for observing characteristics of the combustorflame. Specifically, the optical sensing means is configured to detectspectral and thermal conditions that destabilize the combustion process.

The fuel injector of the subject invention includes an elongated feedarm having means for mounting the injector within the combustionchamber, such as a flange for securing the injector to the interior wallor liner of the combustor. The fuel injector further includes a fuelnozzle or nozzle body, which depends from the feed arm for injecting orotherwise issuing atomized fuel into the combustion chamber forcombustion. In accordance with a preferred embodiment of the subjectinvention, optical sensing means are provided within the fuel nozzle forobserving combustion conditions within the combustion chamber,downstream from the fuel nozzle.

In accordance with a preferred embodiment of the subject invention, thefuel nozzle includes an outer air swirler having a leading edge. Aplurality of circumferentially spaced apart viewing ports are formed inthe leading edge of the outer air swirler. For example, the leading edgeof the outer swirler can include three or more viewing ports spacedequidistant from one another. Preferably, the optical sensing means ofthe subject invention includes a plurality of optical fiber bundles, andthere is an optical fiber bundle accommodated within each of the viewingports formed in the outer swirler. In addition, the optical sensingmeans may further include one or more optical fibers mounted orotherwise supported within a holder along the central axis of the fuelnozzle.

It is envisioned that each embedded optical fiber bundle has a field ofview of between about 14° to 30° (dependent on the fiber NumericalAperture) relative to axis of fiber. Each optical fiber bundlepreferably includes a plurality of optical fibers, and these opticalfibers are oriented so as to extend substantially parallel to thecentral axis of the fuel nozzle. The optical fibers are preferablytreated to withstand the operating temperatures within the combustor.For example, the optical fibers may be provided with a metal coating,such as gold or another precious metal, well suited for thermalprotection.

Each optical fiber bundle is preferably disposed within a temperatureresistant guide tube. For example, the fiber bundles may be disposedwithin stainless steel guide tubes. Preferably, the distal end of eachstainless steel guide tube is cemented within a corresponding viewingport in the outer air swirler of the fuel nozzle in a manner thataccommodates thermal expansion and contraction. This will serve tomaintain the structural integrity of the system through a multitude ofengine operating cycles.

The subject invention is further directed to a system for stabilizingcombustion in a gas turbine engine by observing conditions within thecombustion chamber. The system includes, among other things, opticalsensing means, preferably embedded within each fuel injector, forobserving conditions within the combustion chamber, means for detectingcombustion instabilities based upon conditions observed by the opticalsensing means, and means for modulating the rate of fuel flow to thecombustion chamber to reduce the detected combustion instabilities orotherwise stabilize combustion.

In accordance with a preferred embodiment of the subject invention, themeans for detecting combustion instabilities is adapted and configuredto analyze and process information relating to combustor flamecharacteristics, including thermal and spectral conditions. For example,the means for detecting combustion instabilities may include means fordetecting changes in flame intensity at levels indicative of flameinstability.

Alternatively, the means for detecting combustion instabilities mayinclude means for detecting spectral radiation indicative ofstoichiometric instability. In one embodiment of the subject invention,the detecting means is configured to detect and analyze spectralradiation indicative of chemical emissions effecting flame temperature,NOx, CO, fuel/air ratio and equivalence ratio. It is also envisionedthat the detecting means can be employed in turbine engines fueled bynatural gas. In such instances, the detecting means is configured todetect variability in the natural gas composition that will affect fuelheat values. For example, the detecting means could be configured todetect spectral variations relating to ethane, propane, nitrogen andcarbon dioxide. The system could also be configured to detect thepresence of natural gas contaminants, such as sodium, which can have acorrosive effect on hot engine parts.

The subject invention is also directed to a method of promoting stablecombustion in a gas turbine engine. The method includes the steps ofobserving a combustor flame from a location upstream from the flame todetect spectral characteristics indicative of one or more conditionsaffecting combustion stability, and subsequently tuning the engine tostabilize combustion based upon an indicated condition effectingcombustion stability. In one embodiment of the subject invention, thestep of observing a combustor flame includes the step of detectingchanges in spectral intensity indicative of flame instability. Inanother embodiment of the subject invention, the step of observing acombustor flame includes the step of detecting spectral radiation peaksor emissions indicative of stoichiometric instability. Those skilled inthe art will readily appreciate that the step of tuning the engine tostabilize combustion includes adjusting the fuel flow and/or air flow tothe combustion chamber, or otherwise the fuel to air ratio forcombustion.

The subject invention is also directed to a fuel injector having anoptical sensor that includes an optical rod formed from a material thatis capable of withstanding the temperatures associated with flameexposure within the combustion chamber of a gas turbine engine. Theoptical rod has an optical surface positioned in such a manner so as togain flame exposure sufficient to oxidize soot deposits thereon.Preferably, the optical rod is an optically transparent sapphire rodthat is located at least partially within a viewing port formed in thefuel nozzle. The rod extends from the surface of the nozzle a distancethat is sufficient to enable the optical surface of the rod to be inclose proximity to the combustor flame. This facilitates the oxidationof soot deposits on the optical surface of the rod. It is envisionedthat the optical surface of the optical rod is coated with a catalystthat enhances or otherwise promotes the oxidation of soot and that theoptical surface of the optical rod is a frosted surface that acts as adiffuser to increase the acceptance angle of radiation from thecombustor flame or otherwise expand the field of view of the sensor.

These and other aspects of the apparatus, system and method of thesubject invention will become more readily apparent to those havingordinary skill in the art from the following detailed description of theinvention taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those having ordinary skill in the art to which the presentinvention pertains will more readily understand how to employ the novelapparatus, system and method of the present invention, embodimentsthereof will be described in detail hereinbelow with reference to thedrawings, wherein:

FIG. 1 is a schematic representation of an active combustion controlsystem for a gas turbine engine configured in accordance with apreferred embodiment of the subject invention;

FIG. 2 is a graphical illustration of a spectral scan generated by acomputer based spectrometer using optical data obtained by observingconditions within the combustion chamber of a gas turbine engineutilizing the optical sensing array of the subject invention.

FIG. 3 is a side elevational view, in cross-section, of the combustionchamber of a conventional gas turbine engine, which includes fuelinjectors containing the optical sensing array of the subject invention;

FIG. 4 is a perspective view of a fuel injector constructed inaccordance with a preferred embodiment of the subject invention, locatedwithin the combustion chamber of a gas turbine;

FIG. 5 is an enlarged perspective view of the fuel nozzle, which formspart of the fuel injector of FIG. 4, with sections of the outer airswirler removed to reveal the optical fiber bundles for viewingconditions within the combustion chamber;

FIG. 6 is a side elevational view of the lower portion of the fuelinjector of FIG. 4 depicting the field of view of the fiber bundlesembedded within the fuel nozzle;

FIG. 7 is a graphical illustration of a spectral ratio scan generated bya computer-based spectrometer using optical data obtained by a pair ofoptical fibers located centrally within the fuel injector nozzle of thesubject invention;

FIGS. 8 a through 8 c illustrate three different methods of terminatingan optical fiber bundle in accordance with the subject invention; and

FIG. 9 is a perspective view of a portion of the fuel nozzle of thesubject invention, wherein the optical sensor includes a sapphire rodhaving a frosted optical surface which acts as a diffuser and which islocated in close proximity to the combustion flame to promote oxidationof soot deposits that accumulate thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals identifysimilar features or aspects of the subject invention, there isillustrated in FIG. 1 an active combustion control system configured inaccordance with a preferred embodiment of the subject invention, anddesignated generally by reference numeral 10. The active combustioncontrol system 10 is designed to reduce thermo-acoustic combustioninstabilities within the combustion chamber of a gas turbine engine. Thesystem is intended to lower engine emissions, improve engine dynamicsand maximize operating efficiency. The active combustion control systemof the subject invention is particularly well suited for use incombustion systems that are inherently unstable such as, for example,industrial gas turbine engines wherein lean premixed combustion is usedto reduce NOx, and high power thrust augmented military aircraft engines(afterburners) which utilize locally rich combustion.

Referring to FIG. 1, active combustion control system 10 includes aplurality of fuel injectors 20, described in detail below, which deliveratomized fuel to the combustion chamber of a gas turbine engine at acontrolled rate of flow. There are two primary types of atomizing fuelinjectors, and either type of injector may be employed with the systemof the subject invention. These devices include swirl pressureatomizers, which derive energy for atomization from fuel pressure, andair blast atomizers, which derive energy for atomization from highvelocity compressor air. Examples of atomizing fuel injectors aredisclosed in U.S. Pat. No. 6,688,534 to Bretz, the disclosure of whichis incorporated herein by reference in its entirety.

The fuel injectors 20 each include a plurality of optical sensors 30 inthe form of an array for observing conditions within the combustionchamber of a gas turbine engine, such as, for example, the thermal andspectral stability of the combustor flame. These optical sensors 30 areembedded in or otherwise integral with the fuel injectors 20, and arewell adapted for prolonged service within the highly corrosive, hightemperature environment of a gas turbine combustion chamber, as will bedescribed in greater detail below.

The active combustion control system 10 of the subject invention furtherincludes an electronic signal processor 40. Signal processor 40 isadapted and configured to analyze and process real-time data receivedfrom or otherwise transmitted by the optical sensor array 30 associatedwith each of the fuel injectors 20. This real-time optical data isprimarily used to detect combustion instability within the combustionchamber of the gas turbine engine, including conditions relating tospectral and/or thermal stability.

Preferably, the signal processor 40 includes a signal-generating device45, which generates output signals based upon the data received from theoptical sensors 30. The signal generator 45 is preferably filtered so asto acquire energy in a narrow spectral band relating to an emission froma specific chemical species or radical. Alternatively, it is envisionedthat the signal generator could be filtered in such a manner so as toacquire energy is a plurality of specific spectral bands, each of whichrelates to an emission from specific chemical species or radical.

In one embodiment of the invention, the signal processor 40 may includeone or more filtered photo multiplier tubes (PMT) for electronicallyamplifying a light signal. For example, the signal processor can includeeight different filtered PMT's. Alternatively, signal processor 40 mayinclude one or more filtered silicone photodiodes each with an integraloperational amplifier.

A photodiode is a solid-state device that detects light and creates acurrent flow between doped forms of silicon in response thereto. Incomparison, the sensitivity of a PMT may be adjusted and it provides afaster response than a photodiode. Furthermore, PMT's are designed todetect relatively weak signals as compared to photodiodes. However,photodiodes are cheaper, more robust and more readily available in awider variety of wavelengths than PMT's. Nevertheless, these types ofsignal generators are considered to be interchangeable and both providereliable output signals for detecting conditions effecting combustionstability. The type of signal generator employed will depend upon thesignal strength, wavelengths to be detected and cost.

The output signal generated by signal processor 40 undergoes an analysisto detect conditions effecting spectral and/or thermal instability,which are root causes of combustion instabilities. The analysis isperformed by a computer-based spectrometer, which is operativelyassociated with the signal processor 40. A suitable spectrometerpreferably has a range of between 180 and 800 nm, and is programmed orotherwise configured to derive flame quality parameters relating tocombustion stability, such as flame stability and flame temperature, aswell as the presence of fuel contaminants, fuel components and chemicalemissions or radicals.

In one embodiment of the subject invention, the signal processor 40 andassociated spectrometer are programmed or otherwise configured to detectand analyze changes in flame intensity. These changes are indicative ofthe combustion driven pressure oscillations, which cause combustioninstability in a gas turbine engine. It is envisioned that the opticalsensor array 30 and/or signal processor 40 would be calibrated undernormal engine operating conditions, so that variations in opticalintensity or optical signal amplitude with respect to the variations inthe intensity of the instability would be evaluated based uponcalibrated values. A spectral scan generated with the optical sensorarray 30 of the subject invention and depicting variations in spectralintensity with changes in fuel to air ratios is illustrated in FIG. 2.Upon detecting variations in spectral intensity indicative of anunstable operating condition, the fuel flow rate could be adjusted ormodulated to stabilize combustion.

In another embodiment of the subject invention, the signal processor 40and associated spectrometer are configured to detect spectral radiationindicative of chemical emissions effecting combustion stability. Moreparticularly, signal processor 40 is programmed to detect and analyzethe ratio of OH chemiluminescence peaks (occurring at about 310 nm) andCH chemiluminescence peaks (occurring at about 430 nm) observed byoptical sensor array 30, as illustrated in FIG. 2. This information isthen correlated to the flame temperature, NOx, CO, fuel/air ratio orequivalence ratio. This emissions feedback is then used to tune theengine to a stable operating condition, such as by adjusting the fuelflow, air flow and/or fuel to air ratio for combustion.

In yet another embodiment of the subject invention, the signal processor40 and associated spectrometer are programmed or otherwise configured todetect and analyze spectral radiation indicative of fuel contaminants orimpurities effecting fuel heat values. This is of particular importancein turbine engines powered by natural gas, since natural gas istypically an unpurified fuel. It is well known that variability in thecomposition of natural gas can affect fuel heat values. For example,variations in the amount of ethane, propane, nitrogen and carbon dioxidecan cause heat value to vary. It is also known that the presence ofsodium in natural gas can have a corrosive affect on hot engine partssuch as the combustor itself and turbine blades. Changes in fuel heatvalues can cause a gas turbine engine powered by natural gas to becomede-tuned and can jeopardize the stability of the combustion process.Upon detecting spectral emissions or radicals indicative of the presenceof certain fuel contaminants or impurities, the engine can be tuned to astable operating condition.

With continuing reference to FIG. 1, the signal processor 40 isoperatively associated or otherwise in communication with a fuelinjector controller 50. The fuel injector controller 50 is adapted andconfigured to receive a conditioned signal from processor 40. Based onthis signal, the fuel injector controller 50 commands or otherwisecontrols the flow of fuel to each of the fuel injectors 20 to reduce orotherwise correct a detected condition effecting combustion stability.For example, the fuel controller 50 could command a pulsed or modulatedfuel flow to the fuel injectors to stabilize combustion. Alternatively,fuel controller 50 could be configured to adjust the fuel to airratio/concentration for combustion.

Referring now to FIGS. 3 and 4, the fuel injectors 20 of the subjectinvention are mounted or otherwise supported within the combustionchamber 60 of gas turbine engine 70 in a conventional manner. Moreparticularly, each fuel injector 20 includes an elongated feed arm 22having a support flange 24 for mounting the injector within thecombustion chamber 60. The support flange 24 is particularly adapted tosecure the injector to the interior wall or liner of the combustionchamber using conventional fasteners. The fuel injector 20 furtherincludes an inlet port 25 for receiving fuel from a fuel pump at adesired flow rate. A fixed or variable displacement vane pump may beemployed. A fuel nozzle 26 depends from the distal end of feed arm 22and is designed to inject or otherwise issue atomized fuel into thecombustion chamber 60. As noted above, a fuel injector 20 can take theform of a pressure atomizer or an air blast atomizer. In eitherconfiguration, the fuel nozzle 26 includes an outer air swirler 28configured to impart an angular component of velocity to the air flowingthrough the nozzle body.

Referring now to FIGS. 5 and 6, in accordance with a preferredembodiment of the subject invention, the optical sensors 30 describedbriefly above are provided, located or otherwise embedded within theouter air swirler 28 of fuel nozzle 26 for observing combustionconditions within the combustion chamber 60 of gas turbine 70,downstream from the fuel nozzle. To accommodate the optical sensors 30in a non-intrusive manner, a plurality of circumferentially spaced apartviewing ports are formed in the leading edge 32 of the outer air swirler28, creating an optical sensor array. For example, as best seen in FIG.4, the leading edge 32 of the outer swirler 28 can include three viewingports 34, which are preferably spaced substantially equidistant from oneanother (e.g., about 120° apart), and an optical sensor 30 isaccommodated within each viewing port 34.

Those skilled in the art will readily appreciate that the number ofviewing ports formed in the outer air swirler 28 of the fuel nozzle 26can vary from one nozzle type to another, and/or from one engine type toanother. For example, four viewing ports spaced 90° apart from oneanother can be provided in a particular nozzle body constructed inaccordance with the subject invention. It should also be understood bythose skilled in the art that the optical sensors disclosed herein canbe embedded in other parts of the nozzle body, other than the outer airswirler, without departing from the spirit or scope of the subjectinvention. That is, depending upon the type and structure of the nozzlebody, the location of the embedded sensors can vary, so long as theyhave an adequate field of view downstream from the fuel nozzle, andremain non-obtrusive in that they do not negatively affect the overallperformance of the fuel nozzle.

It has been found through experimentation that disposing the opticalsensors 30 at the leading edge 32 of the fuel nozzle 26 is advantageous,since the combustor flame will remain within the line of sight or fieldof view sensors, thus providing a fairly accurate representative map ofthe flame zone. It has also been found that positioning the opticalsensors 30 at a plurality of spaced apart locations around the leadingedge 32 of the fuel nozzle 26, thus forming an optical sensor array,will allow specific modes of combustion instability to be observed anddetermined. By knowing the specific form of the instability, moreeffective control can be achieved.

The optical sensors 30 are defined, in pertinent part, by optical fiberbundles 36. An optical fiber bundle 36 consists of a plurality ofindividual optical fibers 38. This provides redundancy in case offailure, more efficient energy transfer to the signal processor 40, andallows for a broader field of view relative to the combustor flame. Inaddition, an optical fiber bundle is easily bent to accommodate contoursof the fuel nozzle.

It is envisioned that each optical fiber bundle 36 has a field of viewdefined by angle θ of between about 14° and 30° relative to axis offiber, as best seen in FIG. 6. It is also envisioned that the opticalfiber bundles 36 can be split or otherwise configured such thatindividual fibers within each bundle will observe different spectralwavelengths within their field of view.

In one embodiment of the subject invention, each optical fiber bundle 36includes three individual optical fibers 38. The optical fibers 38 areaimed or otherwise oriented so as to extend generally parallel to thecentral axis of the fuel nozzle 26, as best seen in FIGS. 4 and 5. Ithas been determined that this orientation provides the broadest field ofview with respect to the combustor flame. Those skilled in the art willreadily appreciate however, that the specific orientation of the fiberbundles can vary depending, for example, upon the geometry of the fuelnozzle.

The optical fibers 38 forming fiber bundles 36 can consist of 100μsilica (UV enhanced) fibers or the like. The fibers 38 are preferablycoated or otherwise treated to withstand the operating temperatureswithin the combustion chamber 60. These temperatures can exceed 500° C.For example, the optical fibers 38 may be provided with a coating, suchas gold or a similar precious metal suited for thermal protection. Othercoatings resistant to high temperatures may also be used.

Each optical fiber bundle 36 is disposed within a temperature resistantguide tube 42 for additional thermal protection. For example, the fiberbundles 36 may be disposed within stainless steel guide tubes or asimilar protective structure. The distal end of each guide tube 42 isswaged to secure the fibers therein, and cemented within a correspondingviewing port 34 in a manner that accommodates thermal expansion andcontraction. For example, ceramic cement may be used to secure thedistal end of each guide tube 42 within a viewing port 34. This willensure the integrity of the fiber bundles throughout a multiplicity ofengine operating cycles. The guide tubes 42 are preferably embedded inor otherwise mounted to the feed arm 22 of fuel injector 20. Forexample, the guide tubes may be positioned within channels formed in thefeed arm 22 of fuel nozzle 20. The proximal end of each fiber bundle 36terminates at a location external to the combustion chamber 60 in aconventional optical connector (not shown), which is suitable forreception by signal processor 40.

Referring to FIG. 5, in addition to the plurality of optical fiberbundles 36 positioned within the viewing ports 34 formed in the outerair swirler 28 of the fuel nozzle 26, an optical sensor 80 may bemounted along the central axis of fuel nozzle 26 to increase the overallfield of view and functionality of the system. Optical sensor 80 canconsist of one or more coated optical fibers. For example, opticalsensor 80 can consist of one or more gold-coated 400μ silica (UVenhanced) fibers or the like.

In one embodiment of the subject invention, optical sensor 80 is axiallymounted within the fuel nozzle 26 by a supporting fixture associatedwith the inner air swirler (not shown). In this position, sensor 80 isutilized to detect variations in spectral ratios indicative ofstoichiometric stability. More particularly, in such an embodiment,optical sensor 80 includes two optical fibers 82 a, 82 b that areaxially positioned in side-by-side relationship to detect variations inspectral ratios of CH output to OH output generated over a period oftime by the signal generator of signal processor 40. For example, asillustrated in the spectral scan of FIG. 7, the relationship of the CHoutput signal to the OH output signal over time, generated bycorresponding PMT's of signal generator 40, can be correlated to changesin fuel to air ratio. Based on this information, the engine will betuned to stabilize combustion. In another embodiment of the subjectinvention, the axially mounted optical sensor can include two opticalfiber bundles, each containing four gold-coated 200μ silica fibers ratedto 700° C.

In accordance with another embodiment of the subject invention, theoptical sensor array 30 of fuel injector 20 is adapted and configured todetect radiation in the infrared spectrum. In this case, the sensorarray is embedded in the fuel nozzle 26 in the same manner described andillustrated above, but one or more of the optical fibers 38 are IRenhanced instead of UV enhanced. In one embodiment, the IR enhancedoptical fibers 38 are adapted and configured to detect spectralradiation in the 1.7μ to 2.1μ range. This correlates to exhaust gastemperature. In contrast, exhaust gas temperature does not correlate tothe chemiluminescence outputs in the UV range described previously.

It has been determined that there is an absorption/emission band forwater vapor generated by the combustion process within the 1.7μ to 2.1μrange. It is envisioned that the output from the infrared sensor arraymay be used to obtain flame temperature, in a manner similar to anoptical pyrometer. It is also envisioned that the output from theinfrared sensor array may be used to obtain turbine inlet vanetemperature when in the field of view.

Referring now to FIGS. 8 a through 8 c, there are illustrated threedifferent methods of terminating the optical fibers 38, which form thefiber bundles 36 within the stainless steel guide tubes 42 located inview ports 34. In one embodiment shown in FIG. 8 a, the optical fibers38 terminate at a location spaced from the distal end of the guide tube42. A shaped lens 90 supported within a frame 92 is joined to the distalend of the guide tube 42. The lens 90 is formed from a material such asapphire and is used to focus or otherwise modify the field of view ofthe optical fibers 38. It is envisioned that the exposed surface of thelens 90 would have a protective coating. For example, the lens can havea vapor deposited layer comprising a mixture of platinum and aluminumoxide which acts as a catalyst to promote oxidation of soot to a gaseousform and thereby reduce contamination of the lens, as disclosed in U.S.Pat. No. 4,521,088 to Masom, the disclosure of which is incorporatedherein by reference in its entirety.

In another embodiment shown in FIG. 8 b, the optical fibers 38 terminateat a location spaced from the distal end of the guide tube 42, and awindow 94 supported within a frame 96 is joined to the distal end of theguide tube 42. The window 94 may be formed from sapphire or a similartransparent material and would function to seal the end of the guidetube from contamination and combustion by-products, which could degradethe optical fibers. It is envisioned that the window 94 could also befrosted or otherwise treated and used as a diffuser to widen the viewingarea of the optical fiber bundle.

In the embodiment shown in FIG. 8 c, the distal ends 38 a of eachoptical fiber 38 in fiber bundle 36 is splayed or otherwise spreadoutwardly so that each individual fiber end 38 a is oriented or directedin a different direction relative to the axis of the bundle. Thisenables the optical fibers to gather light from a broader or greaterarea. Protective coatings could be used to coat the ends of the fibers.

Those skilled in the art will readily appreciate that the bare endedoptical fibers installed within the fuel injector of the subjectinvention, as shown for example in FIGS. 5 and 8 c, as well as the lens90 of FIG. 8 b and window 94 of FIG. 8 c, can become optically obscuredwith soot that tends to build-up over a relatively short period of time,for example, within a few hours. Consequently, the signal obtained bythese optical sensors will become relatively unusable over time.

It is known that soot will begin to oxidize or otherwise burn-off attemperatures of about 400° C., as found in the combustion chamber of agas turbine. However, the material from which the optical fibers 38 offiber bundles 36 are formed cannot readily withstand such combustiontemperatures. Therefore, in accordance with the subject invention,optically transparent sapphire rods, which can readily withstand thetemperatures of combustion and exposure to a combustion flame, arepositioned within each of the viewing ports 44 of fuel nozzle 26, infront of the fiber bundles 36, and extending outwardly from the nozzlesurface. Situated in this manner (i.e., in close proximity to thecombustor flame), soot that has deposited or otherwise accumulated onthe optical surfaces of the rods will oxidize or burn-off when exposedto the combustor flame.

Referring to FIG. 9, each sapphire optical rod 194 extends from theviewing port 44 formed in the outer swirler surface 32 of fuel nozzle 26and is enclosed within a surrounding frame 196. The sapphire rods 194may extend from the swirler surface at a relatively shallow angle.However, it is preferable to orient the optical rods 194 at a relativelysteep angle with respect to the central axis of the fuel nozzle 26.Consequently, the distal end portion of each sapphire rod 194 extendsinto the air stream emanating from the fuel nozzle 26 a sufficientdistance above the surface of the nozzle so that the distal end of therod 194 is relatively close to the combustor flame. As a result, anysoot that is deposited on the optical surface 194 a of the rod 194 willbe oxidized or burned-off by the intense heat of the flame. Each opticalrod 194 has a polished proximal end that is in optical communicationwith a fiber optic bundle 36 located within the viewing port 34.

In an embodiment of the subject invention, the optical surfaces 194 a ofthe sapphire rods 194 that are exposed to the combustor flame orotherwise positioned in close proximity to the flame are coated with acatalyst that enhances the oxidation of soot. That is, the catalyst willpromote the oxidation of soot by lowering the temperature at whichoxidation occurs to a temperature below that which the optical surfaceof the rod is exposed. Such a catalyst may be composed of platinum andaluminum oxide.

In an embodiment of the subject invention, the optical surface 194 a ofeach optical rod 194 is configured to act as a diffuser to increase theacceptance angle of radiation from the combustor flame. Preferably, theoptical surface 194 a of each rod 194 is a frosted surface, which can beformed for example by grinding the surface or by any other techniqueknown in the art that can produce a suitable surface which functions todiffuse light. Consequently, the optical surface 194 a has a virtuallyhemispheric field of view. This allows light or radiation to enter therods 194 from a multiplicity of angles, so that more light is capturedand delivered to the fiber bundles 36 than in other optical sensorsdescribed above. As a result, a larger part of the combustor flame isobserved by the optical sensor, as compared to the part of the flameobserved by the bare-ended optical fibers bundles disclosed herein. Thisin turn provides a greater overall flame intensity control signal. As analternative, the distal end of each sapphire rod can be multi-faceted toexpand the field of view of the optical surface.

In sum, the fiber optic instrumented fuel injector of the subjectinvention may be used for a multiplicity of purposes including, forexample, engine control through detection of combustion instability;fuel to air ratio stability by analyzing spectral relationships;obtaining turbine inlet temperature correlated to flame temperature;detection of fuel impurities based on spectral anomalies; aircraftaugmenter flame detection; obtaining turbine inlet vane temperature byway of a pyrometer; and advanced warning or prediction of lean blowoutconditions.

Although the apparatus, system and method of the subject invention havebeen described with respect to preferred embodiments, those skilled inthe art will readily appreciate that changes and modifications may bemade thereto without departing from the spirit and scope of the subjectinvention as defined by the appended claims.

1. A fuel injector for a gas turbine combustor, comprising: a) a fuelnozzle for injecting fuel into a gas turbine combustor; and b) opticalsensing means operatively associated with the fuel nozzle for observingcharacteristics of a combustor flame, the optical sensing meansincluding an optical rod formed from a material capable of withstandingtemperatures associated with flame exposure, the optical rod extendingfrom a surface of the fuel nozzle and having an optical surfacepositioned in such a manner so as to gain flame exposure sufficient tooxidize soot deposits thereon.
 2. A fuel injector for a gas turbinecombustor as recited in claim 1, wherein the optical rod is an opticallytransparent sapphire rod.
 3. A fuel injector for a gas turbine combustoras recited in claim 1, wherein the optical rod is located at leastpartially within a viewing port formed in the fuel nozzle and extends toa location that enables the optical surface to be in close proximity tothe combustor flame.
 4. A fuel injector for a gas turbine combustor asrecited in claim 3, wherein the optical rod extends at an angle relativeto a central axis of the nozzle.
 5. A fuel injector for a gas turbinecombustor as recited in claim 1, wherein the optical surface of theoptical rod is coated with a catalyst that enhances oxidation of soot.6. A fuel injector for a gas turbine combustor as recited in claim 1,wherein the optical surface of the optical rod is configured to act as adiffuser.
 7. A fuel injector for a gas turbine combustor as recited inclaim 1, wherein the optical surface of the optical rod is a frostedsurface.
 8. A fuel injector for a gas turbine combustor as recited inclaim 7, wherein the optical surface of the optical rod is ground toform the frosted surface.
 9. A fuel injector for a gas turbine combustoras recited in claim 1, wherein the optical rod has a polished opticalend in communication with a fiber optic bundle.
 10. A fuel injector fora gas turbine combustor, comprising: a) a fuel nozzle for injecting fuelinto a gas turbine combustor; and b) optical sensing means operativelyassociated with the fuel nozzle for observing characteristics of acombustor flame, the optical sensing means including an optical rodformed from a material capable of withstanding temperatures associatedwith flame exposure, the optical rod having an optical surfacepositioned in such a manner so as to gain flame exposure sufficient tooxidize soot deposits thereon, wherein the optical rod is located atleast partially within a viewing port formed in the fuel nozzle andextends from a surface of the fuel nozzle to a location that enables theoptical surface to be in close proximity to the combustor flame.
 11. Afuel injector for a gas turbine combustor as recited in claim 10,wherein the optical rod is an optically transparent sapphire rod.
 12. Afuel injector for a gas turbine combustor as recited in claim 10,wherein the optical rod extends at an angle relative to a central axisof the nozzle.
 13. A fuel injector for a gas turbine combustor asrecited in claim 10, wherein the optical surface of the optical rod iscoated with a catalyst that enhances oxidation of soot.
 14. A fuelinjector for a gas turbine combustor as recited in claim 10, wherein theoptical surface of the optical rod is configured to act as a diffuser.15. A fuel injector for a gas turbine combustor as recited in claim 10,wherein the optical surface of the optical rod is a frosted surface. 16.A fuel injector for a gas turbine combustor as recited in claim 10,wherein the optical rod has a polished optical end in communication witha fiber optic bundle.